Titanium in metallic form or as a compound is an important element in the chemical series. For example, titanium dioxide is utilized in paint pigments, in white rubbers and plastics, floor coverings, glassware and ceramics, painting inks, as an opacifying agent in papers, etc. The other titanium compounds are used in electronics, as fire retardants, waterproofing agents, etc. The metal may be used as such or in alloy form as structural material in aircraft, in jet engines, marine equipment, textile machinery, surgical instruments, orthopedic appliances, sporting equipment, food handling equipment, etc. Heretofore in recovering the titanium from titanium-bearing sources such as ilmenite, rutile, etc., the titanium has been subjected to separation steps which involve the formation of titanium as a compound in a valence state of +4, such compounds usually involving titanium dioxide. However, when attempting to separate titanium dioxide from impurities which are also contained in the ore such as iron, the hydrolysis of the titanium dioxide at elevated temperatures usually results in also obtaining relatively large amounts of iron along with the titanium.
Heretofore in the prior art, various methods have been utilized to recover titanium values from titanium-bearing sources.
For example, in U.S. Pat. No. 3,236,596 an unroasted ilmenite ore is leached with hydrogen chloride at an elevated temperature. Following this, dissolved iron is reduced with iron or other reductants to precipitate ferrous chloride by saturating the liquor with hydrogen chloride gas. The hydrogen chloride is then extracted from the liquor by a vacuum distillation and the titanium is recovered by conventional means. Likewise, U.S. Pat. No. 3,825,419 reduces an ilmenite ore to produce ferrous oxides. The reduced ore is then leached for about 4 hours under a moderate pressure thereby dissolving the iron in the acid along with about 15% of the titanium. The iron is recovered as impure ferric oxide by spray roasting the solution while the insoluble leach product which is primarily titanium dioxide but which contains all of the silica present in the original ore is recovered. U.S. Pat. No. 3,859,077 also discloses a process for recovering titanium in which a titanium tetrahalide is mixed with iron oxide in slag or a titaniferous ore at an extremely high temperature of about 1000.degree. C. to produce volatile impurity chlorides and titanium dioxide. A similar patent, U.S. Pat. No. 3,929,962, also reduces a titanium-bearing ore at a high temperature to produce titanium sesquioxide which is in a form whereby it is easier to treat for a titanium-iron separation. Another reference, U.S. Pat. No. 3,903,239, teaches a method for recovering titanium in which unroasted ilmenite is leached over a period of days at room temperature to recover about 80% of the titanium. Sulfur dioxide is added during the leach process to cause a precipitation of the ferrous chloride after which titanium dioxide is recovered by diluting and heating the solution. U.S. Pat. No. 3,076,692 also discusses the problem of minimizing the loss of titanium when leaching to produce titanium in a +4 valence state. The process described in this reference attempts to overcome the loss problem by utilizing a relatively short leach time, i.e. 10-20 minutes, or by adding phosphorous compounds.
In addition to these U.S. patents, U.S. Pat. Nos. 3,897,537 and 3,875,286 are drawn to a process for the beneficiation of ilmenite ores by converting the ore into a pseudobrookite-containing material followed by a reduction of the material to form some ferric iron. The reduction is generally effected by contacting the material with a solid carbonaceous reducing agent such as coal, coke, lignite, etc. or a gaseous reducing agent such as hydrogen, methane, carbon monoxide, etc. However, no mention is made that the excess of the reducing agent is stoichiometric with respect to the iron oxide present in the source material, thus leaving it open to conjecture as to whether the excess is by weight or volume with respect to some other component of the reaction mixture. Additionally, U.S. Pat. No. 3,252,787 describes a process for preparing titanium dioxide concentrated from ilmenite or other similar ores, but is silent as to the criticality of the amount of reducing agent which should be present.
In contradistinction to the prior art methods hereinbefore set forth for recovering titanium metal values from a titanium-bearing source, it has now been found possible to effect a titanium value recovery from a source such as ilmenite in such a manner so that the loss of titanium is minimal in nature.